Cavity tuner



Feb. 28, 1956 E JR 2,736,868

CAVITY TUNER Filed Jan. 11, 1.946

. H 1 I3 1 l9 l6 MI 5 FIG. 3'A INVENTOR PERSA R. BELL,JR.

ATTORNEY United States Patent CAVITY TUNER Persa R. Bell, Jr.,Cambridge, Mass, assignor, by mesne assignments, to the United States ofAmerica as represented by the Secretary of the Navy Application January11, 1946, Serial No. 640,448

13 Claims. (Cl. ass-4:3

This invention relates to high frequency capacitive structures and moreparticularly to variable capacitive devices employed for the purpose oftuning cavity resonators.

Heretofore, capacitive structures when employed for cavity tuning havenot ofiered a wide tuning range and at the same time been simple inconstruction and in operation.

A specific object of this invention is to provide a tuning elementcapable of controlling the frequency of a cavity resonator over a widerange of values.

Another object is to provide a tuning element which can tune a savityresonator over a wide frequency range and with a motion which is bothsimple and susceptible to calibration so as to allow the device to beemployed for such band switching operations as are common in theelectronic art.

A further object is to provide a tuning element which can easily beadapted to the wobbulation of the frequency of a cavity resonator.

A further object is to provide a tuning element which is simple both inconstruction and in operation.

With these objects in view, a cavity tuning element has been devisedcomprising a dielectric rod slideably inserted into a hole provided in awall of a cavity to be tuned, a small metallic fitting, capacitive innature, being mounted on that end of the rod disposed within the cavity.The resonant frequency of the cavity is adjusted by control of the depthof insertion and/or the angle of rotation of the capacitive fitting.

The structural details and features of the present invention aredescribed in the following specification and shown in the accompanyingdrawing of which:

Fig. 1 is a perspective view of one form of the invention;

Fig. 2 is a cut away view of another form of the invention;

Fig. 3 is a cut away view of the structure of the invention inserted inthe resonant cavity of a high frequency oscillator; and

Fig. 3A is another sectional view of the apparatus taken along line A--Aof Fig. 3.

Referring to the drawing and morespecifically to Fig. 1, metallicfitting is shown disposed on an end of rod 11 which may be made of adielectric material such as polystyrene. As shown, said fitting 10 isU-shaped, having two cylindrically curved Walls 12 joined by a curvedend piece 13. The shape of the fittiug'10 mayvary somewhat over thatshown in Fig. 1, but is designed to have a large tuning effect and to benon-resonant within the frequency range over which the structure is tobe used.

In Fig. 1, the fitting 10 is merely pressed into or glued to the end ofrod 11. A more secure means of attaching fitting 14) to rod 11 isprovided by the device of Fig. 2. Herein a recess 14 is made in an endof rod 11, said recess 14 being cylindrically shaped to receive thefitting 10 as shown.

Fig. 3 is a cut away view showing the tuning structure of Fig. 2inserted into the cylindrical resonant cavity 18 of a McNallyoscillator. Fig. 3A is another sectional view of the same structure. Asis well known, the cavity 18 of a McNally oscillator is external to theglass seals 15 and is electrically connected to the internal structureof the tube by metallic disks 16.

A hole is drilled radially into the cylindrical cavity 18 and midwaybetween the top and bottom of said cavity. This hole is made largeenough to receive the rod 11, and any of a number of well-knownsupporting and clamping structures may be employed to hold and allowpositioning of the rod 11.

As is clearly shown in Fig. 3A, the walls 12 of the fit ting 10 form twocylindrical capacitors with the surfaces 19 of the cavity 18. These twocapacitors are connected effectively in series by the end piece 13 ofthe fitting 10 (Fig. 3), and their magnitude is controlled by the depthof insertion and the angle of rotation of the fitting 10. The end piece13 of the fitting contributes only a negligible inductive efiect, andthe capacitance between the walls 12 of the fitting 10 is small.

The rod 11 functions principally as the position controlling means ofthe tuning element, but with the structure of Fig. 2, also serves as thedielectric medium of the two variable capacitors formed.

In the apparatus of Figs. 3 and 3A, the resonant frequency of the cavity18 is lowered by the introduction of the tuning element of thisinvention. Maximum tuning effect is had when said element is fullyinserted and when angularly positioned as shown in Fig. 3A.

A form of the invention comprises a cavity resonator having amultiplicity of capacitive tuning devices of the type shown in Fig. 1.The tuning means of this invention is obviously not limited toapplication to McNally cavities alone.

It will be apparent to those skilled in the art that the resonantfrequency of the cavity structure shown in Fig. 3 may be wobbulated inany number of ways such as by continuous or back and forth rotation ofthe rod 11 about its longitudinal axis, or by an in and out motion ofthe rod 11 relative to the cavity 18. It can also be seen that thetuning structure of Fig. 3 can be calibrated in terms of frequency andthat said device may be adapted to the discontinuous switching from oneresonant frequency to another.

The invention described in the foregoing specification need not belimited to the details shown, which are considered to be illustrative ofonly one form the invention may take. What I desire to secure by LettersPatent and claim is:,

1. In combination, a tuning element comprising a cylindrical dielectricrod having a U-shaped capacitive member fixedly secured to one endthereof, and a cylindrical cavity resonator having conducting wallsurfaces, the distance between the top and bottom inside surfaces ofsaid cavity being slightly less thanthe diameter of said dielectric rod,a hole having a diameter slightly greater than that'of said dielectricrod being disposed radially in said cavity and midway between the topand bottom walls thereof, said dielectric rod being slideably engaged insaid hole so as to support said U-shaped capacitive member inside saidcavity.

2. A tuning element for a cavity resonator comprising, a conductivemember substantially in the form of a hollow cylinder having one openend and one end closed by a substantially hemispherical surface, saidconductive member being formed with two diametrically opposed slotsextending from said open end of said cylinder to points adjacent saidclosed end of said cylinder, said slots extending in a directionsubstantially-parallel to the axis of said cylinder, a dielectric rod,the axis of said rod being coincident with the axis of said cylinder,said dielectric rod being mechanically secured to said conductivemember, and means for supporting said dielectric rod so that at least aportion of said conductive member reciprocates within said cavityresonator.

3. A tuning element for a cavity resonator comprising, a conductiveU-shaped member having two substantially parallel sidepieces and acurved endpiece joining said two sidepieces, said two sidepieces beingin the form of curved, elongated strips lying on a common cylindricalsurface, said sidepieces being disposed diametrically opposite eachother, a cylindrical dielectric rod, said U-shaped member being securedto an end of said dielectric rod with the axis of said cylindricalsurface coincident with the axis of said dielectric rod, and meansassociated with said cavity resonator for supporting said dielectric rodwith said U- shaped member at least partially within said cavityresonator, said supporting means being adapted to permit predeterminedadjustive movement of said U-shaped member relative to said resonator.

4. In combination, a cavity resonator having first and second spacedconductive end walls, a portion of each of said end walls being formedto conform to the surface of a circular cylinder, said cylinder havingan axis extending between said walls and substantially parallel theretoand a tuning element, said tuning element comprising a conductive membersubstantially in the form of an elongated, hollow, circular cylinderhaving one open end and one curved, closed end, said conductive memberbeing disposed in spaced relationship to said cylindrically formedportions of said end walls with the axis of said conductive membercoincident with the axis of said cylindrically formed portions of saidend walls, said conductive member being formed with two diametricallyopposed slots extending parallel to the axis thereof from said open endto points adjacent said closed end, said tuning element furthercomprising a dielectric rod secured to said conductive member, saiddielectric rod being slidably and rotatably supported by said cavityresonator.

5. In combination, a cavity resonator having first and second spacedconductive end walls, a portion of each of said end walls being formedto conform to the surface of a first circular cylinder, said cylinderhaving an axis extending between said walls and substantially parallelthereto, and a tuning element, said tuning element comprising aconductive U-shaped member having two substantially parallel sidepiecesand a curved endpiece joining said two sidepieces, said two sidepiecesbeing in the form of curved, elongated strips lying on a secondcylindrical surface having an axis coincident with the axis of saidfirst cylindrical surface, the diameter of said second cylindricalsurface being smaller than said diameter of said first cylindricalsurface, said sidepieces being disposed diametrically opposite eachother, a cylindrical dielectric rod, said U-shaped member being securedto an end of said dielectric rod with the axis of said rod coincidentwith the axis of said second cylindrical surface, said dielectric rodbeing slidably and rotatably supported by said cylindrical portions ofsaid end walls.

6. In combination, a cavity resonator having first and second spacedconductive end walls, a portion of each of said end walls being formedto conform to the surface of a first circular cylinder, said cylinderhaving an axis extending between said walls and substantially parallelthereto, and a tuning element, said tuning element comprising anelongated cylindrical dielectric member slidably received saidcylindrically shaped portions of said end walls, said dielectric memberbeing formed with a cylindrical axial opening therein at the end thereofextending between said end walls, and a conductive U- shaped memberdisposed within said cylindrical opening in said dielectric member, saidconductive member being formed with two substantially parallelsidepieces and a curved endpiece joining said two sidepieces, said twosidepieces being in the form of curved, elongated strips conforming tothe circumference of said cylindrical opening in said dielectric member,said sidepieces being disposed diametrically opposite each other, saidclosed end of said U--shaped member being disposed adjacent to the endof said dielectric member extending between said end walls.

7. A tunable cavity resonator comprising a resonating chamber formed bytwo, spaced, substantially parallel, conductive end plates and aconductive wall member joining said end plates to enclose the volumetherebetween, the spacing between said plates being substantially lessthan at least one lateral dimension of said end plates, a portion ofeach of said end plates being formed to conform to the surface of acircular cylinder, said cylinder having an axis extending between saidend plates and substantially parallel thereto, and a tuning elementextending through said wall member and into said resonating chamber,said tuning element comprising an elongated, cylindrical dielectricmember, slidably and rotatably received between said cylindricallyshaped portions of said end plates, said dielectric member being formedwith a cylindrical axial opening therein at the end thereof extendingwithin said resonating chamber, and a conductive U-shaped memberdisposed within said cylindri cal opening in said dielectric member,said conductive member being formed with two substantially parallelsidepieces and a curved endpiece joining said two sidepieces, said twosidepieces being in the form of curved, elongated strips conforming tothe circumference of said cylindrical opening in said dielectric member,said sidepieces being disposed diametrically opposite each other, saidclosed end of said U-shaped member being disposed adjacent to the end ofsaid dielectric member within said resonating chamber.

8. In combination, a cavity resonator having first and second spacedconductive end walls, a portion of said end walls being formed toconform to the surface of a circular cylinder, said cylinder having anaxis extending between said walls and substantially parallel thereto,first and second conductive members disposed in spaced juxtapositionwith said cylindrically formed portions of said first and second endwalls, respectively, means supporting said members in said juxtaposedposition, said supporting means being adapted to permit lateral movementof said members with respect to said cylindrically formed portions androtational movement of said members about said axis, and meansconductively coupling said two members.

9. A tuning element for a cavity resonator comprising, a conductingU-shaped member, the legs of said U-shaped member having curved surfaceslying along a common cylinder, the bight of said U-shaped member alsohaving a curved surface, and a dielectric rod having a cylindrical axialrecess in one end thereof, said U-shaped member being disposed withinsaid recess with its bight adjacent the open end of said recess.

10. A tuning element for a cavity resonator comprising, a cylindricaldielectric rod, an axial recess in one end of said rod, and a U-shapedconductive member positioned within said recess, whereby the arms ofsaid U-shaped member and the Walls of said cavity resonator form twoseries connected capacitors, the material of said rod functioning as thedielectric medium in said capacitors.

11. In combination, a resonant cavity having a pair of spaced walls,tuning means for said resonant cavity comprising, a U-shaped memberforming with said spaced walls two series capacitors, and means forrotatably and reciprocally mounting said U-shaped member, said meanscomprising polystyrene material enclosing said U-shaped member andserving as the dielectric in said capacitors.

12. A tuning elementfor a cavity resonator comprising a polystyrene rod,an axial recess in one end of said rod, and a conductive U-shaped memberpositioned within said recess, the legs of said U-shaped memberconforming to the inner wall of said recess and the bight of said 5 6U-shaped member lying adjacent the open end of said References Cited inthe file of this patent mess- UNITED STATES PATENTS 13. In combinatlon,a resonant cavity, tuning means therefor comprising, a U-shaped memberforming with 2'226479 PuPP 1940 the walls of said cavity two seriesconnected capacitors, 5 2,262,020 Llewellyn 1941 and means mounting saidU-shaped member for rotation- 2,280,824 Hansen 1942 al and translationalmovement to thereby vary the fre- 2,401,489 Lmdenblad June 1946 quencyof Said cavity 2,417,542 Carter Mar. 18, 1947 2,442,671 Tompkins June 1,1948 10 2,513,205 Roberts June 27, 1950

